Anode structure



Nov. 5, 1 957 T. w. MALTBY ET AL 2,812,462

ANoDE STRUCTURE Filed May 18, 1953 @j @2 l@ ,Y

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ANDD STRUCTURE A; Truman W. Maltby, Pirmasens, Germany, and Howard Electric Company, a corporation of .New York Application May 18, 1953, Serial No. 355,617 n 3 Claims. (Cl. 313-55) The present invention relates in generalto electronics, and has more particular reference to electron iiow devices, such as X-ray generating tubes, the invention relating, in its specific aspects, to an improved electrode construction especially Well suited for anti-cathodic service in X-ray generating tubes. y 1 j X-rays may be generated by causing the impingement of electrons, emitted from a suitable cathode, upon an anti-cathode or anode, such cathode and anode -being usually enclosed within a sealed, evacuated envelope and comprising an X-ray generating tube. Electron impingement upon a target surface of the anode, at relatively high velocity, constitutes the target surfacevas a source of X-rays, at the zone or area of electron impingement, the so generated X-rays being emitted thence through and outwardly of the enclosing envelope as a useful beam of X-rays.

For certain purposes, as in the application of X-rays to diffraction analysis, it is desirable not only to control the production of a sharply defined X-ray beam, but also to exclude from said beam all X-rays other than rays of predetermined character. In this connection, it should be understood that X-rays emitted from the anode of a generating tube provide a continuous spectrum, the characteristic wave length and distribution of which de-l pends upon the material employed as an electron target, every target material having its own characteristic X-ray spectrum, which is independent of the operating potential applied between anode and cathode of the generating tube, above a minimum voltage, which minimum voltage is also characteristic of the particular target material involved. l

Any suitable target material may, of course, be employed for X-ray ditraction analysis, providing that the target material and its characteristic X-ray spectrum are known, as otherwise spectral lines produced by the target material, in the spectrograph of the material under examination, may be mistaken for lines supposedly caused by the material being examined. The choice of a suitable target Vmaterial forVX-ray diffraction analysis depends, to a considerable extent, upon the nature of the material to be examined, the particular examination technique em ployed, and the type of information sought. lt'is obvious that, regardless of technique or the nature ofthe material under examination, a` prerequisite for accurate' analysis is :the productionv of an X-ray beam" containing onlyX-rays of selected spectral characteristics. I An important objectof the' present invention, therefore,

isl to control the emission of an X-rayV beam fromthe' anode of a generating tube in fashlon producing a rela# tively'sharply defined ray beam'comprising only rays of desired spectral character, while excluding from the beam substantially all contaminant rays having 'different or' undesired spectral characteristics. A further object of the invention is to provide animproved anode structure, shaped and configurated in novel fashion and adapted, inv conjunction withcooperating apertured orw'slitt'ed shield means,v to control emissionA from nited States Patent 2,812,462 Ice Patented No 5, 1957 2 theanode lof a generating tube, of a narrow, sharply de# fined X-ray beam comprising only rays of desired spectral character. j p

Another important object is to providean anode having an electron target surface including a central target portion of limited area, lying in position to receive elec- W. Pickett Wauwatosa Wis., assgns to General vtrons'directed thereon from a cooperating cathode, and

anode portions surrounding said central target portion anddisposed rearwardly thereof, whereby X-rays gen-l erated through electron impact on said target portion may be emitted thence through apertured screen means as a sharply defined beam, while unwanted rays, generated by electron impact upon anode surfaces, outwardly ofthe central target portion, may be directed outwardly of and thus excluded from said well defined beam.

Another important object is to provide an anode having electron target surface portions of truncated conical or pyramidal configuration providing a central apexial surface portion lying in a plane transversely of the central axis ofthe'pyramid, and surfaces extending outwardly of lsaid apexial surface portion and rearwardly or downq wardly thereof, said surfaces making angleswith said apexial surface of at least 15; a further object being to provide an anode having an apexial target surface portion of preferably elongated configuration, whereby the anode mayA be employed in combination with an `elongated g cathodic electron emission source disposed in spaced apart facing alinement with the longitudinal axis of the elongated apexial surface area of the anode. y Another important object is to provide, in conjunction with an anode of the character mentioned, a suitable slit structure for the transmission of a useful X-ray beam anodes embodying the inventiongand.

produced by electron impact on the target surface portion of the anode while excluding transmission, in the direction of said beam, of X-ray produced by electron impact on anode surfaces outwardly of said target surface p0rtion; a further object being to provide an anode enclosing shield or screen of material relatively opaque to X-rays, and provided with window openings or slits substantially in alinement with the plane of the central target portions of the anode, whereby to block transmission, past said shield, of rays other than those generated as lthe result of electron impact on the central target portion of the anode. I The foregoing and numerous other importantV objects, advantages, and inherent functions of the invention will become apparent as the same is more fully understood fromthe following description, which, taken in connection with the accompanying drawings, discloses 'a' pre-V ferred embodiment of the invention.

' Referring to the drawings:

Figs. 1-4 are diagrams illustrating the manner of generating X-rays as Vthe result of cathode ray electron impact upon an anodic electron target;

Fig. 5 is a face View of an anode ent invention; Figs. 6 and 7 are sectional views taken substantially along the lines 6-6 and 7-7 in Fig. 5;

Fig; 8 is a sectional view taken through an X-ray generator fitted with an vention;

Figs. 9k and l0 are sectional views illustrating modified embodying the pres-v Fig. l1 is an end View of the anode shown in Fig. 10. `As shown more particularly in Fig. 1 of the drawings, X-rays may be generated at the target surface S of an anode A, as the result of impingement thereon ofy an.

electron E, emitted from a cathodic emission element C.

Such generated rays are emitted uniformly in all directions radially of the point of impact ofthe electron E on the target. -X-rays thus emitted, as shown in dotted lines y in-Fig. l, in the hemispherical zone behind the plane of anode embodying the present in-Y the target surface, are usually substantially completely attenuated or absorbed by the material of the anode target.

Rays emitted, as shown in solid lines in Fig. 1, within the hemispherical zone in front of the vtarg'etsurface, n'ay be put totuscful service:

v When the cathodic emission element C is in operati'oxt,l it will, of course, as shown more particularly in Fig. 2, emit continuously a stream or cloudr of electrons ina direction causing electron impingernent upon the anode substantially throughout the entire area of the surface S thereof which4 faces toward the emission element. The anode of an X-ray generating tube commonly pro'videsu more or less sharply defined focal area within the 'anode surface Sand upon which electrons emitted .by the ele'-I inent C are caused to im'pinge, it being desirable to focus the electron beam as Vsharply as possible to causeelect'ron impingement only within the limited focal area, in order that generated X-rays may emanate principally from said fo'calarea and not to any substantial extent as the result of electron impact upon the anode surfaces outwardly of the focal area. The focal area may be and is commonly defined b'y the exposed surface of a `'target button Tof desiredtarget materiaL, which may be embedded `in the body of the anode in position exposed at the surface S thereof which faces toward the emission element C.

The Atarget end of the anode, however, may comprise homogeneous material, in which case the focal area merely comprises a zone or spot within the target surface S of the anodewhich faces the electron emission element- Electron ow control means may be and commonly is provided for causingh impingement of the electron beam within theufocal area of the anode. As a consequence, the major portion of the electron beam normally comprises a stream of focused electrons F, all of which may impinge upon the anode withinthe focal area thereof, and stray or marginal electrons M which impinge upon the anode outwardly of the focal area.

Each electron, when it impinges upon the anode target surface S, whether the same be a focused electron ,Fi which impinges within the focal area of the anode, or a stray electron M, which impinges upon the marginalportions of the anode surface S outwardly of the f oalarea, generates X-rays in the manner illustrated in Fig. 1;,and such Xfrays, in the aggregate will.` include not only rays having the spectral characteristics of the electron target material of the anode within the focal area, but also the` spectral characteristics ofthe anode material `outwardly of its said tar'get area.k

In usingX-rays for diffraction analysis, asrshown more particularly in Figs. 2 and 3, a baille or screedv B'of substantially X-ray opaque `material may be employed in conjunction with the anode, s'aidbale 4preferably yen. closing the anode on all sides thereof and `having an aperture'or opening O, usually contgurated` as aiperforation or slit in `the baffle. Such a bafe may'con'trol they emission of a sharply defined usefulray vbearn Xthrough the bathe aperture O, which beam may be 4applied for the diffraction analysis of a material sample Wf-t'o be analyzed; If desired, the `arlalyzing beam Xmaybe'delivered upon the test sample W through Brentano, slit- Figs. 1, 2, and 3,\will not only include X-rays P, shownin! solid lines inFig. `3f, generated as the result` of electronV impingement upon the focal area of the anode, such rays R consequently having the desired spectral'characterisitiesY ofthe target material comprisingsaid focal area,hb`ut the, ray X may also include undesirablerays Q, shown in flottedylinesV in Fig. 3, produced through impingement-'of stray electrons M upon the anode surface S outwardly of within the envelope.

the focal area and hence providing undesirable `spectral characteristics in the ray beam X, where the material of the anode outwardly of the focal area is of a sort having undesirable spectral characteristics.

To illustrate the present invention, Figs. 4-8 show an X-ray generator 11 comprising a sealed and evacuated envelope 12 containing an anode 13 and a cathode structure 14 having a head 15 in facing relationship with the anode within the envelope. The cathode embodies an electron emitting element 16, which may comprise an elongated filament adapted to be electrically excited for the emission of electrons, as by electrically connecting the filament with a suitable 'source of exciting power outwardly of the envelope, the filament, to that end, being electrically connected with conductors 17 extending outwardly of the envelope 12, through suitable conductor seals, and electrically connected, as with terminal means l'forthed or supported on the envelope for electrical connection with an external power source.

I t will be noted that the preferably elongated emission element 16 is supported in a groove 19 formed in the head 15, whereby electrons, emitted by the filament, when energized, will be focused upon an elongated area ofthe cathode facing portions of the anode 13. To aid in thus focusing the electron stream upon the anode, the cathode structure may include a skirt-like bafe or shield 20 electricallyconnected with and projecting from the head V15, in position encircling and enclosing the facing end of the anode. It isdesirable, thus, to focus or concentrate impinging electrons as sharply as possible within what `may be termed the focal area of the target surface of the anode, in order that generated X-rays may emanate from such well defined focal area and thereby allow for theproduction ofuseful X-ray beams of sharp definition.

The anode 13 may comprise a metal body 21,` as of copper Aor other suitable material, supported on the envelope 12, as by means of a mounting 22, the body having a stem 23 extending outwardly of the envelope. The body 21 is supported in the envelope in position presenting an end of the body in spaced facing relationship with respect to the cathode, and the anode may include a head 24` integrally united with the body 21, at its cathode facing end, said head comprising any suitable or preferred target material and providing electron receiving target surfaces facing toward the cathode.

Any suitable or convenient source of external electrical power may be employed to cause electrons emitted by the element 16 to travel toward and impinge upon the target surfaces-of the-,anode headt24. To this end, said external power source Vmay be electrically connected between one of the conductors 17 and the Vprojecting stem portion 23` of the anode, outwardly of the envelope, in order to apply lelectron driving potential between the electron emissionclement 16 and the anode head 24, said head being electrically 'connected with the body 21 and the portion 2?:V thereof which extends outwardly of the envelope.

X-rays 'generated` at the target end of the anode as a result of electron impingernent thereon may travel in all directions radially outwardly of the target. In the interests of safety, itis desirable to permit only such rays as are required for -use to escape outwardly of the envelp'e. To this end, the envelope 12 preferably, though not essentially, `may comprise glass which is substantially impervious `to X-rays, in order to prevent egress of unusable or unwanted Xrays outwardly of the envelope 12;

Inorder-to insure the retention of unwanted X-rays, an annular; sleeve 29 may also be provided in position surrounding Ethe envelope 12 opposite the electron receiving end of the anode, said sleeve Vcomprising material `opaque to-X-raysj-for the ,purpose of confining unwanted rays It is desirable, however, to allow all-useful X-rays to have substantially unhampered exit from theiX-raysource. To this end, the envelope may be formed with drawn necks 30, providing envelope openings angularly displaced around the envelope with respect to the target portions of the anodi and'the skirt-like shield 20 may be formed with openings or slits'31in 'alinement with the envelope openings defined by the necks 30, the'shield 20 being preferably supported on the cathode head in position presenting said slits 31 substanto pass outwardly of the envelope in unimpeded fashion through the slit or slits 31 and the envelope openings defined by a neck or necks 30 of the envelope.

The space within the envelope, of course, is necessarily maintained at low pressure, and, in order'to seal the 'envelope at the openings defined by the necks 30, suitable X-ray pervious window panes 33 may be sealed on the necks in position closing the openings defined thereby. Such X-ray pervious panes may comprise disks or plates of material, such as beryllium, which is substantially transparent to X-rays.

The divergence of ray beams employed .fin diffraction analysis normally ranges up to about fouri angularA degrees. As heretofore shown, slit systems, which permit such divergent ray beams to reach a diffraction analysis sample, from anodes of conventional configuration, must necessarily allow radiation to reach the sample from electron impact stations or areas of the anode outwardly of the focal spot area, in addition to those rays which originate from the focal spot area itself.

For purposes of accuracy and precision in X-ray diffraction analysis, it is desirable to apply, to the body being examined, only such X-rays as originate at the focal spot of the anode, and exclude such rays as may be generated by electron impingement on the anode target areas outwardly of the focal spot or area.` Since itis virtually impossible to so focus electrons, emitted from theelement 16, as to insure impingement of all emitted electrons only in the focal spot area, it is obvious thatat least some of the electrons emitted by the element 16 will strike upon the anode portions outwardly of the focal spot area, and result in the generation of so-called off-focal spot radiation at the places or stations of impact of electrons, such as the electron 26', on the anode outwardly of the focal spot area. The present invention has for its principal object the provision of means whereby such off-focal spot radiation may be prevented from reaching a diffraction analysis specimen through a divergent ray beam slit system, even where divergence is of an order as large as tentangular degrees. Y Y

To this end, the anode head 24`is provided with a central focal spot area25, which comprises a` at target surfacel disposed preferably at right angles to the'raxis of a beam of electrons 26 emitted by the element 16, although the principles of the present invention may, of

" course, be applied inV X-ray generators in which: the.. focal spot area of the anode is disposed in a plane other than normal with respect to the electron beam emitted by the cathode. Where the emission element 16 is of elongated configuration, the focal spot area 25 may be of corresponding, substantially rectangular, elongated configuration, although the invention, of course, is not necessarily limited to the marginal shape or configuration of the Zone or area 25, which may have circular, oval or other shape, if desired.

Immediately outwardly of the at anode target surface forming the focal area 25, the anode is formed with surfaces which extend away from the cathode in such fashion that all anode portions outwardly of the focal area lie behind planes extending at angles of the order of l`a` or more with respect to'the plane of the focal area. As shown, the anode surface portions outwardly of the zone 25 may comprise a pair of oppositely sloping surfaces 27 extending at and outwardly of the zone 25, on the opposite sidesk thereof, and a pair of oppositely sloping surfaces 28 extending at and outwardly of the opposite shape.

ends of the `zone 25. The cathode facing portions of "the anodhead 24 Athus comprise' a body vof 'truncated pyramidal configuration, consisting of the apexial surface area 25 forming the focal area ofthe anode target and the pyramidal side surfaces 27 and 28 outwardly of the apexial area and sloping at angles of the order of or more in a direction away from the electron emission element 16 of the cathode. The invention, however, is n'ot necessarily limited to the pyramidal configuration of the anode head, butin its broader aspects, may include the formation of the head 24 as a truncated element of conical configuration providing a target area of circular or oval Indeed, the anode surfaces, immediately outwardly of the target zone, may if desired include portions extending at any desired inclination with respect `to the plane of the target area in excess of 15.

The divergent ray beam 32, produced by impact of electrons comprising the focused beam 26 upon the focal spot area 25, may thus be'delivered through the slit 31`and thence outwardly of the envelope 12 through a window pane or panes 33 substantially without obstruction. Any

rays, such as the rays 34 generated at and emitted by the anode as the result of electronl impingementV upon the marginal anode surfaces outwardly of the focal area 25, will not be transmitted through the slit 31 in a direction coincident with the path of the ray beam 32, since such v marginal surfaces diverge from the plane of the focal area at angles preventing emission of the rays 34 in the direction of the useful ray beam 32.

YIn this connection, it should be understood that the angle of divergence of the inclined target surface portions of the anode outwardly of the focal spot area 25 need be only sufficiently large as to assure that all rays generated through electron impact on the anode, outwardly of the focal spot area, be emitted from the anode in a direction other than within the vzone occupied by the useful divergent ray beam 32. The invention, accordingly, is not necessarily limited to a particular inclination or shape of the anode surfaces outwardly of the focal spot area 25, so long as anode configuration outwardly .and rearwardly of the focal area is such as to accomplish the desired result.

l target material, such as tungsten,`may be venveloped-"or yotherwise secured in the material. of the head 24, in posi- -tion -exposed at the focal spot area 25 of theanode, head.

In such an arrangement it is desirable to form the button 35 so that it may include marginal target surface portions 36 extending outwardly of the central focal area 25. Such an arrangement will result in producing a useful ray beam 32 having spectral characteristics corresponding Vonly with the material of the button 35, and excluding unwanted rays 34 having the spectral characteristics of the anode material forming the head 24 outwardly of the button 35.

The inclination of the surfaces 27 and 28 is not critical so long as such surfaces are disposed at inclinations greater than the angle at which none fo the rays 34 extend within the useful beam 32 at the zone or stati-on where the same is applied to perform a useful function, as at the slit means R, or at the specimen W under examination in the event that the useful beam 32 is applied directly to the specimen.

As shown more especially in Fig. 9, the inclined surfaces 28 may make substantial angles with respect to the target surface 25, thereby providing a shouldered configuration Eigs.f10 and 11 show thatthe invention, if desired,

`may be incorporatedin an anode having acathode lfacing `end of generally circular configuration.

Theabove described anode structure has manifold advantag'es, especially ,where ,employed in X-ray generator tubes forf.ditfractionu analysis in accordance with the r Brentano parafocusing` technique. Anodes embodying the H.present invention ,providegreater spectral purity, jespef cially when the target Asurface as iscommonlythevcase..

comprises a targetbutton 35 of the selected target mate-y` ,.,rial surrounded byanotherandditerent metal compris- ,ingttheremaining portions of the head 24. Greater spec ptralqpurity. is also attained ybyminimizing the apparent v4intensity of,tungsten radiationinathe spectrumbfrays .emittedby the anode,.the tungsten spectrum resulting from :deposits ofsuch metalupon the anodeA outwardly'of thefocal areaZSasthe result of evaporation ofthe usually t tungsten filament 16 during the service life of the generator tube. Thepresent inventionthus substantially reduces n nbackground aberration inthe, spectrum of; rays produced- U.by Vtheyoperation of the tube, and'thus narrows the base offditfraction lines` and produces diffraction` patterns of higher contrast and resolution.

" Theinvention is `herebynclaimed as follows:

1.l An` X-ray. generator tube comprising an anode havming altarget `end, :a `cathode spaced from and r`facngthe l targetend ofr the anode, and a sealed, evacuated envelope enclosing said anode and cathode, the target end of said anode providing a ufocal` surface lying in a-flat plane for reeeivingthe: impact of.,electrons emitted rby the cathode ofthe-tube, baie means formed with an aperture slitv A:therein -for defining and. transmittingoutward1y of the u 4anode and substantially in thesdirection` of the plane of saidfocal-surface, a` beam of'X-rays suhtending an `angle of not morethan 10 at thecenter of;said focal sur- V facefsaidanode having peripheral target portionsextendf ing; at-tand-,outwardlyof vthe marginaledges ofsaidfocal f: surface; and lying entirely behind a plane intersectingl the 4fimarginalwedge 0f said focalsurface at an inclination, with n-frespect to the plane` thereof,such that X-raysV generated L by=electron impact.` upon said peripheral target portions Will'be emittedthence in'directions other than coincident with" thebeam "jof" X-rays delivered' through said slit. Y 2. An" X-ray generatory tube comprising an anode having a target end, abat-bode spaced from aud facingthe targetend of ;the.anode,` and a sealed, evacuated envelope 'enclosingsaid anode, and cathode, the target end of said anode providing a focal surface lying in a at plane for receiving the impactfof electrons emitted by the cathode gof; the `rtube, and bale means forming an aperture slit ,therein for defining and transmitting, outwardly of the anode and substantiallyin the plane thereof, `a beamof X-rays emitted at "saidsfocal surface and subtending an angle of S` or -1ess,said,anode having peripheral target portionsextending at and outwardly of the marginal edges of saidy focal surface andlyingentirely behind a `plane intersecting `the'mvarginal edge of said focal surface at;an inclination, with respect to the plane thereof, such that X-rays, generated by electron impact upon said periph eral target portions will 'be emitted thence in directions ,other-than coincident withthe 4beam of X-rays delivered through said slit.

,. 3. An X,-ray generator tubecomprising an anode having `atargebend, a cathode vspaced from and facing the ,target endet-the anode, `and a sealed, evacuated envelope i, enclosingsaid Vanodeand cathode, the target end of said anode providing a focal ,surface lying in a at plane for areceivingthe impact offelectrons emitted by the cathode of the tube, and a` baiein position screening said anode ,and formedzwith, anaperture slit for defining and transmitting, .outwardly of` thefanode and substantially in the .l directionof'theplane of said focal surface, a beam of Xfrayssubtending an angle of the order of 5 at the center Y yof'said focal surfacesaid `anode having peripheral target 'portionsextending at vand outwardly of the marginal edges V- ofsaidffocal surface and lying entirely `behind a plane -,-.intersecting the. marginal, edge of said focal surface at an I inclination-with Arespect to the plane thereof, suchthat X-rays generated by electron impactupon said perpiheral target` portions `will be emitted thence in directions other ,iv than coincident rwith the beam of X-rays delivered through 1 said slit.

References Cited in the file of this patent `UNITED STATES PATENTS 1,215,116 4Coolidge Feb. 6, 1917 A1,685,928 Morrison Oct. 2, 1928 '1,708,494 11 Bucky Apr. 9, 1929 2,232,831 Van Der Duuk et al Feb. 25, 1941 2,311,725 Atlee Feb.\23,'1943 f' 2,336,271 `Ma'chlett` et al. Dec. 7, 1943 2,345,722 Atlee Apr. 4,1944

- FOREIGN YPATENTS -'"671,576 :Germany Feb. 13,1939 

